Re: CSS3 Text and UAX14

On 2/20/2007 3:55 AM, Paul Nelson (ATC) wrote:
> CSS is a higher level protocol. There is room for a higher level protocol to override things, for example, by specifying the PRE.
>  
> I think the issue with UAX14 is that it specifies what the normal line breaking behavior should be for scripts. I would much rather rely on following guidelines in UAX14 for normal behavior and then override things based on CSS author desires.
>  
>   
>>   1. Spaces are a non-tailorable line breaking class. The description
>>      of its behavior also includes prescriptions on presentation that
>>      are not compatible with what CSS prescribes.
>>     
>
> The only place where I see problems with the SP definition are in the PRE situation where we are keeping the widths of all spaces explicitly. In this case are we really tailoring the line breaking class of the character? 
>   
I think PRE is not an issue. The only time you get an issue is when you 
use "CRT-style" line breaking at a fixed column so that SP can get 
wrapped to the head of a new line. CRT-style line breaking is clearly 
not UAX-14 compliant, and should therefore be labeled as such (an 
non-UAX14 compliant mode with special behavior)

The descriptions in UAX#14 of how the *width* of SPACE characters is 
handled are informative material on line-layout, not specifications of 
line-breaking.
 
>>   2. CSS has a line breaking mode that forbids all breaks. This needs to
>>      override the non-tailorable behavior of the ZW (and SP?) classes.
>>     
>
> In this case, CSS is simply saying that the line has no end, and therefore there is no wrapping point. We are not overriding the behavior of the ZW and SP classes.
>   
Elegant way of putting that.  That formulation avoids creating a new mode.
>  
>   
>>   3. CSS3 Text introduces an 'unrestricted' line breaking mode. In this
>>      mode, line breaking restrictions are ignored completely, (except for
>>      the CM class). 
>>     
>  
> One way to look at the 'unrestricted' line breaking is that we are forcing emergency line breaking to happen at the end of every line. 
>   
Same. Seen in this light, my earlier remarks about the difference 
between CM and non-spacing marks would apply.

This is a very productive way of looking at the issue of these 'special' 
modes in a way that doesn't require them to be handled as rules in UAX#14.

A./

Received on Tuesday, 20 February 2007 22:33:36 UTC